In the field of infrared spectroscopy, a KBr (potassium bromide) tablet method is frequently used, as disclosed in Patent Documents 1 and 2. In the KBr tablet method, initially, a desired solid sample in the form of powder or thin film is retained by a pellet prepared by compression-molding potassium bromide powder. Then, the pellet retaining the sample is irradiated with light, whereby a transmission spectrum or an absorption spectrum is obtained. Since potassium bromide easily transmits infrared light having a wave number of not less than 500 cm−1, potassium bromide is suitable for spectrometry in this band. In spectrometry in a band including wave numbers of not less than 250 cm−1, cesium iodide is often used as a material for the pellet.
In recent years, spectrometry utilizing terahertz waves, which are the waves in a lower wave number band than the above-described band including a wave number of 250 cm−1, is gaining attention and being studied. It is considered that this terahertz spectrometry can detect absorption due to intermolecular interaction, hydrogen bond and Van der Waals force and hence provide characteristic information which cannot be obtained by spectrometry in other wave number bands. However, the transmittances of potassium bromide and cesium iodide with respect to terahertz waves of such a low wave number band are low.
Conventionally, therefore, pellets prepared by compression-molding polyethylene powder are actually used in the terahertz wave spectrometry. Since polyethylene pellets have higher transmittances with respect to terahertz waves than potassium bromide pellets or cesium iodide pellets, the use of polyethylene pellets is preferable for obtaining proper spectrum data.
However, the use of such a polyethylene pellet has the following drawbacks.
Taking glucose as an example, there are two forms of glucose, which are a hydrate, i.e., combined with water molecules, and an anhydride, i.e., not combined with water molecules. When a glucose hydrate is subjected to spectrometry as a sample, a spectrum influenced by water molecules is obtained which is different from a spectrum of an anhydride. Since terahertz waves are easily influenced by water molecules, the difference between the spectrum of a hydrate and that of an anhydride is noticeable in this wave number band.
As will be understood from the above-described example of glucose, even from basically the same substance, different spectrum data is obtained depending on whether the substance is a hydrate or an anhydride. Further, even from samples both of which are hydrates, the spectrum data differs due to the difference in water content therebetween. For this reason, the process for identifying a sample based on the spectrum data is complicated and difficult. Therefore, such problems need to be solved.
Patent Document 1: JP-A-5-232018
Patent Document 2: JP-A-11-166891